Turbine systems include buckets extending radially outward from rotor wheels. The buckets generally include a root portion, a substantially planar platform, and an airfoil portion. To increase the efficiency of the turbine systems, increased operating temperatures and materials which can withstand the increased operating temperatures are continually being sought. As advancements in materials are made, the construction and/or configuration of the buckets can change.
One material advancement includes the development of non-metallic buckets such as ceramic, ceramic matrix composite (CMC), or metal matrix composite (MMC) buckets, which have increased temperature capability as compared to metal and/or metal alloy buckets. Although the increased temperature capability of the non-metallic buckets would increase the efficiency of existing turbine systems, the non-metallic buckets often have differing root portions from existing metal and/or metal alloy buckets. For example, non-metallic buckets often include a dovetail-shaped root portion, whereas the metal and/or metal alloy buckets they are replacing often include a conventional fir tree-type root portion.
Many existing turbine systems have wheels or rotors that are configured to receive the conventional fir tree-type root portion of the metal and/or metal alloy bucket, and not the dovetail-shaped root portion of the non-metallic buckets. As such, many current turbine systems do not permit direct field replacement of existing metal and/or metal alloy buckets with non-metallic buckets without excessive cost and additional complexity. Furthermore, thermal expansion of the non-metallic buckets differs from the thermal expansion of the metal and/or metal alloy buckets. Attaching the non-metallic bucket to the rotor wheel configured to receive the metal and/or metal alloy bucket may cause damage to the metal and/or ceramic at their interface, as the materials expand at different rates leading to damage of the bucket where attached to the rotor wheel.
A turbine system and adapter that do not suffer from one or more of the above drawbacks would be desirable in the art.